1. Field
One embodiment of the invention relates to a system, such as an Internet Protocol (IP) telephone system, which makes voice communications among terminals via an IP network. More specifically, the present invention relates to a communication which determines normality and confirms presences of terminals connected to the IP network and driven by a battery, and to server apparatus and terminal apparatus.
2. Description of the Related Art
In recent years, a network telephone system (IP telephone system) which transmits/receives images and voices as interactive packet data in real time has begun to be widely used. Storing a plurality of IP telephone terminals in the IP network such as a local area network (LAN) and the Internet, and also connecting the IP network to a public network via a gateway to perform address conversions at the gateway, the IP telephone system permits multimedia information communications among the IP telephone terminals with one another, and among the IP telephone terminals and the public network.
In this case, before making communications, transmitting connection confirming signals such as keep-alive signals to each terminal and making the terminals send back their response signals result in performing the normality determinations and presence confirmations of the terminals. The foregoing IP telephone system transmits the connection confirming signals from the communication server even to the gate way to make the gateway send back its response signal then obtains the normality determinations and presence confirmations of the terminals (for instance, refer to Jpn. Pat. Appln. KOKAI Publication No. 2002-335290).
By the way, the aforementioned system allows multimedia information communications even among small-sized portable terminals and the IP telephone terminals. In such case, the system executes normality determinations and presence confirmations for the telephone terminals such as battery-driven terminals and IP telephone terminals under the same condition. In particular, in the battery-driven terminals, frequent times of execution of the normality determinations and presence confirmations of the terminals results in an increase in consumption power and causes a reduction in terminal waiting time.